Why is there an annoying red word that says 'demo' on my tablet screen and wont go away?

A

AC Question

there is a annoying red word that says demo on my tablet screen and wont go away

My tablet is only a month old, this is why you don't buy **** designed from andriod makers.
Ugh I need this tablet for school but this DEMO won't go away. I turned it off and then when I turned it on, it wouldn't go away. I tried resetting everything , deleting everything.

PLEASE SOMEONE HELP MEEE